The present invention relates to improvements to a rotary positive-displacement pump for fluid products.
The invention has been developed with particular but not exclusive regard to a pump for use in machines for dispensing colouring agents for the production of paints, varnishes, inks and the like.
Positive-displacement pumps of the rotary type having internal gears are known. One of these pumps is illustrated in FIG. 1 appended to the present description and is the subject of patent IT-1292625 belonging to the same applicant, the content of which is regarded as incorporated by reference in the present description. The known pump illustrated comprises a rotor 13 mounted on the end of a main shaft 12. The rotor 13 has peripheral teeth 15 that can mesh with teeth 16 of an idle sprocket 17 which is supported in rotation by a pin 18 of a conveying body 19.
Despite the generally satisfactory operation of the above-mentioned known positive-displacement pump, in a few particular cases some malfunctions have been encountered which have led to the jamming of the idle sprocket 17 on the pin 18 and of the rotor 13 inside the cylindrical cavity 11a of the body 11 of the pump (illustrated diagrammatically in FIG. 1). In particular, the above-mentioned malfunctions have occurred when the positive-displacement pump has been used with some types of colouring product that, owing to the particular chemical composition, promote the creation of a sticky film. It has been found that this sticky film can penetrate and become wedged between the idle sprocket 17 and its support pin 18, and also between the outer curved surface of the rotor 13 and the associated cylindrical housing 11a in the body 11 of the pump, until it causes the complete jamming of the rotating elements.